A standard mixing valve (see U.S. Pat. Nos. 4,621,659 and 4,540,023 and German patent document 3,318,888) used in a single-lever faucet has a normally cylindrical housing centered on an axis and a valve plate closing the bottom of the housing and formed with a hot-water inlet port, a cold-water inlet port, and an outlet port. A control plate carried on a backing plate sits flat atop this valve plate and is formed with a cavity that normally overlies the outlet port and that can also be brought into registration over the inlet ports, either singly or jointly. A lever pivoted on the housing is connected via the backing plate to this control plate to slide and rotate it atop the valve plate, thereby determining the amount of overlap of the control-plate cavity with the inlets to determine the amounts of hot and cold water to be shunted through this cavity to the outlet port.
Although the confronting faces of the normally ceramic control and valve plates are normally machined to perfect smoothness and planarity and are greased, it is standard as discussed in German patent document 3,244,120 to provide a lip-type seal surrounding the ports of the valve plate. Such a seal is of V-or X-section with the arms of the V or X lying against the confronting faces of the control and valve plates.
The main problem with such a seal is that the lips can get caught in the gap that can form between the plate faces. Such wedging not only holds the two plates apart, but can lead to damage of the seal.